1. Field of the Invention
The present invention relates to a trajectory generation apparatus for generating a trajectory of a robot.
2. Description of the Related Art
A robot is controlled to move along a trajectory generated in advance. The trajectory of robot can be generated by a trajectory generation apparatus. The trajectory generation apparatus generates a trajectory based on teaching points and a speed specified by an operator. For example, the operator inputs teaching points generated in advance to the trajectory generation apparatus. The trajectory generation apparatus generates trajectory passing through or near the teaching points.
In this regard, when a robot is driven at the specified speed along trajectory generated by trajectory generation apparatus, a load applied to the robot becomes larger in some cases. According to the conventional techniques, when the load applied to the robot is large, the speed of the robot is reduced.
Japanese Laid-open Patent Publication No. 10-69310 discloses an apparatus for generating a trajectory for a robot which obtains a realizable moving speed when a tip portion of a robot passes the inside of a teaching point and calculates a deceleration rate with respect to the moving speed recorded in teaching point data. It is disclosed that at an operation of the robot, the robot is operated by being decelerated according to deceleration rate of an inward turning portion.
Japanese Laid-open Patent Publication No. 2014-14876 discloses a robot control apparatus which divides a movable range of a robot arm into multiple spaces and sets a constraint value of jerk so that load torque falls within an allowable range in each of the multiple spaces. It is disclosed that a calculating unit generates an instruction value to an electric motor so that the robot arm follows a specified trajectory.
When a robot is accelerated, decelerated, changes a direction, or the like, a load is applied thereto. For example, a large force is applied to a transmission of a driving apparatus for driving joint units of the robot. In particular, a larger load is applied to the robot when being driven on a curved portion of a trajectory than when being driven on a straight line portion of the trajectory. There is a problem that, when an operation of the robot is continued under an excessive load, the life of the robot is shortened.
As described in Japanese Laid-open Patent Publication No. 10-69310, when a load is large, the robot can be decelerated to reduce the load. In particular, a curved portion of a trajectory, the robot can be decelerated to reduce the load. However, there is a problem that reduction of a speed of the robot prolongs a cycle time of the robot. In other words, there is a problem that an operation time of the robot is prolonged.
On the other hand, an operator may want to increase the speed of the robot rather than to be precise in the trajectory. In other words, it is preferable in some cases to drive the robot without reducing the speed as much as possible even if the trajectory is slightly separated from desired teaching points. In particular, a deceleration rate becomes larger at the curved portion of the trajectory at which a larger load is applied to the robot, and thus it is preferable to make an operation of the robot faster at the curved portion of the trajectory.